Optical spectroscopic observations of blazars and gamma-ray blazar candidates in the Sloan Digital Sky Survey Data Release Nine

TL;DR

This study uses SDSS DR9 optical spectra to classify blazars and gamma-ray candidates, confirming classifications, estimating redshifts, and identifying new gamma-ray blazars, thereby improving our understanding of these energetic sources.

Contribution

It introduces a statistical method to identify optical counterparts and classifies uncertain blazars, also confirming redshifts and discovering new gamma-ray blazar candidates.

Findings

Confirmed classifications for 20 ROMA-BZCAT blazars

Estimated redshifts for 18 blazars

Identified 8 new gamma-ray blazar candidates

Abstract

We present an analysis of the optical spectra available in the Sloan Digital Sky survey data release nine (SDSS DR9) for the blazars listed in the ROMA-BZCAT and for the gamma-ray blazar candidates selected according to their IR colors. First, we adopt a statistical approach based on MonteCarlo simulations to find the optical counterparts of the blazarslisted in the ROMA-BZCAT catalog. Then we crossmatched the SDSS spectroscopic catalog with our selected samples of blazars and gamma-ray blazar candidates searching for those with optical spectra available to classify our blazar-like sources and, whenever possible, to confirm their redshifts. Our main objectives are determining the classification of uncertain blazars listed in the ROMA-BZCAT and discovering new gamma-ray blazars. For the ROMA-BZCAT sources we investigated a sample of 84 blazars confirming the classification for 20 of them and obtaining 18 new redshift estimates. For the gamma-ray blazars, indicated as potential counterparts of unassociated Fermi sources or with uncertain nature, we established the blazar-like nature of 8 out the 27 sources analyzed and confirmed 14 classifications.